Actually, I think you'll find a wide variety of clear coats being used by builders here, not just envirotex
Flex coat, devcon 2 ton, systems three, etc. Might be worth finding out what clear coat your friend used on the plugs and how well that holds up. May not need anything else. No matter what clear coat you use, the plug is, hopefully
, going to get beat up. Additional clear coats may also alter the plug weight some too.
Jigman